Today, in a wide range of fields of product management, position detection, and the like, one-dimensional codes, two-dimensional codes, and other optical codes written with information expressed by symbols having reflectance different from that of the periphery are used. The one-dimensional code, which is also referred to as bar code, linear code, or the like, can express information, such as alphanumeric characters, for example, a universal product code through its bars and spaces made using striations with different widths linearly arranged adjacent to each other. The two-dimensional code, which is also referred to as two-dimensional symbol or the like, is a symbol in which information are arranged vertically and horizontally so that high information density is achieved, thereby storing a larger amount of information than the one-dimensional code. Note that the QR code (registered trademark) is a type of two-dimensional code.
To read optical codes, such as one-dimensional codes or two-dimensional codes, a code scanner or other optical information reading apparatuses is used. Optical information reading apparatuses are widely used in different fields. For example, an optical information reading apparatus is attached to a movable body which is called a vehicle in a transfer system. In this case, the optical information reading apparatus moves with the vehicle and reads an optical code attached to a predetermined position (station), and upon success of reading, outputs code information to the processor of the vehicle. The code information acts as a trigger for vehicle's deceleration or stop.
In use of the optical information reading apparatus, the stability of reading the optical code decreases due to contamination on the code label, print quality deterioration, contamination on the reading window of the optical information reading apparatus, or the like. Conventionally, a process is performed for measuring reading stability and outputting predictive maintenance information (PMI) indicating reading stability (see PTL 1).
Since the optical information reading apparatus notifies the user of the fact that the reading stability is decreasing at the stage where the optical code is readable, the user can take a necessary countermeasure before the optical information reading apparatus can no longer read the optical code, thereby avoiding the situation where the optical code unintentionally becomes unreadable.